Generally, the invention of this application relates to filtering an air stream. Specifically, the invention relates to improvements to the technique of removing gaseous, liquid, and solid contaminants from an air stream with an aqueous-froth as described in parent application Ser. No. 09/889,225, incorporated herein by reference.
The key aspect of the present invention is the novel combination of using “nucleation” in concert with an aqueous froth (shown best in FIGS. 3A-3G). In the “nucleation” technique, the incoming contaminated air stream is saturated with a fine mist produced by fogger nozzles, causing supersaturation of the air stream. The sub-micron contaminants act as condensation nuclei in the supersaturated air stream, in much the same fashion in which rain droplets are formed. The contaminants become encased in an airborne fluid aerosol. The encased contaminants are “trapped” inside bubbles continuously formed in an aqueous froth. Finally, the bubbles carrying the encased and trapped contaminants are collapsed or coalesced in a controlled fashion. The contaminants, in the form of large condensates, are easily deposited into a liquid decontamination reservoir.
The filter of the present invention will effectively remove particles as small as 0.005 micron in diameter, including such agents as Industrial sulfate aerosols, biological agents such as Corona virus with a mean diameter of 0.07 microns, Variola major (Smallpox virus) with a mean diameter of 0.2-0.3 microns, chemical weapon agents such as VX, HD, Sarin, Mustards, radiological aerosols, as well as larger agents such as anthrax spores.
Aside from other advantages, such as low maintenance cost and low energy consumption, the combined nucleation and aqueous-froth air filter of the present invention has no minimum pore size found in conventional air filters. It essentially mimics the atmospheric water cycle.
According to the present invention, a contaminated air stream is saturated with a fine mist generated with specially designed fogger nozzles. This produces a range of very small droplet sizes quickly supersaturating the incoming air stream. Although the Kelvin curvature effect limits the size of a cloud droplet in the atmosphere, the controlled conditions inside the aqueous-froth air filter enable smaller droplet and vapor formation without the limiting/counteracting effects of evaporation found in nature.
A key operational point here is that sub-micron contaminants in the air act as condensation nuclei causing heterogeneous nucleation, effectively encasing the contaminants in an airborne fluid aerosol. Bubbles are then generated using the incoming contaminated supersaturated air stream, making controlled supersaturated encapsulated micro-atmospheres. In addition to heterogeneous nucleation, the controlled micro-atmosphere in the bubbles also encourages collision coalescence, reduces mobility of target aerosols, and prolongs contact between the decon solution and the contaminants. In a subsequent stage, the air is cooled forcing additional internal condensation and controlled bubble collapse, as well as coalescence. The resulting large condensate is then easily deposited into the liquid decontamination reservoir in the same manner as raindrops forming, thereby removing contaminants from the air stream and safely containing them in the decon solution. An additional dehumidification stage ensures that any leftover aerosols are removed and trapped prior to the clean decontaminated air stream exiting the stage.
The filter is capable of extremely high efficiency, wet or dry, super-micron and sub-micron aerosol removal, and is ideally suited for filtering particles in the 0.1 micron range. It should therefore be an excellent high efficiency filter for removal of hazardous aerosols of interest.
The present invention is capable of removing hazardous radiological aerosols as well as removal and neutralization of chemical and biological aerosols. The unit will have operating costs significantly lower than HEPA systems and will have higher efficacy. The projected unit cost in mass production is under one thousand dollars. This cost effective implementation of the invention should easily scale to large systems.
Existing air filters are inadequate for current as well as emerging threats. There is an urgent need to develop efficient low cost air filtration methods capable of high efficiency removal of aerosolized chemical and biological weapon (CBW) agents as well as radiological agents from contaminated air. This is a challenge as these agents exist in aerosol, vapor, or particulate form in a wide range of sizes.
Current state-of-the-art air filtration technology is based on sixty year old technology. HEPA/ULPA filters use permeable substrates in an air stream to trap particles. Problems with this technology include high energy and maintenance costs, limitations on the effective particle size that can be filtered at high airflow, and increase in operation cost and degradation of performance over time. HEPA filters are relatively ineffective on CW (chemical weapon) agents, and trapped BW (biological weapon) contaminants remain active, thus such filters must be disposed of as hazardous waste. Other filtration techniques require using combinations of technologies increasing cost, complexity and mass, whereas a single filter of the present invention should be sufficient for mitigating NCBW (nuclear, chemical, biological weapon) threat.
The aqueous-froth filter, shown in Ser. No. 09/889,225, can remove large quantities of nuisance dust generated while sanding when finishing gypsum wall panels. A portion of the nuisance dust is sub-micron in size. Although all perceivable contaminants are removed from the air stream, sub-micron contaminants not present in macroscopic amounts can be drawn through the aqueous-froth air filter and build up in the vacuum source. Sub-micron contaminants can stay suspended in the air, inside the bubbles of the froth, until the bubble wall is absorbed by the wet surfaces of the saturated fiber element, or torn between the surface tension with wet surfaces of the filter and the surface friction of the bubble in the air steam. If the contaminated air inside the bubble is released at the top of the froth column, near the saturated fiber element, sub-micron contaminants can pass through the saturated fiber elements to the vacuum source.
The present invention provides, among other things, an aqueous-froth filter which includes nucleation techniques to more thoroughly filter super and sub-micron contaminants from an air stream. Air filter protection from hazardous aerosolized contaminants; chemical, biological, and radiological weapons of mass destruction, or relief from smog (for example acid aerosols), allergens (bio-active aerosols), and undesirable sub-micron particulates (abrasives, corrosives) require a more complete and reliable method to urge contact and coalescence between sub-micron contaminants, the wet surfaces of the aqueous froth, and the filtering solution than the original aqueous-froth filter, shown in parent application Ser. No. 09/889,225. Additionally, the horizontal airflow design requires a reliable, low-maintenance, continuous-duty, means of limiting the froth to a predetermined volume that is independent of the turbulence in the solution reservoir.